In the assembly of microelectronic and micromechanical packages and other assemblies, solder is used to make electrical connections for thermal connection and for physical attachments. A package can have several different solder connections that are made at different times. Similarly, a printed wiring board, case and other devices can also have several different solder connections that are all made at different times. Each solder connection is made by applying heat to melt the solder and make the connection. Frequently reflow ovens are used which heat the entire system to melt the solder onto the connection.
When the device is constructed, care must be taken to ensure that previous soldering is not damaged by later soldering. If a first solder joint is made and then the device or the solder joint is heated beyond the melting temperature of the first solder joint, then the first solder joint may be damaged.